Astronomers may have been listening for alien civilizations in only a small slice of the radio spectrum — and a new study using archived data from the ALMA telescope in Chile suggests a largely unexplored range of higher frequencies deserves attention.
Traditional SETI searches have mostly tuned in around 1.4 gigahertz, the frequency of the cosmic hydrogen line. The new team, led by SETI researcher Luigi Mason, instead scanned two spectral windows around 90-93 GHz — frequencies more than 60 times higher, which advanced civilizations might favor because they offer far more bandwidth.
The survey examined four archived ALMA observations, including nearby stars, and found no narrowband signals of artificial origin. But the bigger result is methodological: it demonstrates that high-frequency radio telescopes built for other purposes can be repurposed to search for extraterrestrial intelligence.
The work significantly expands the number of stars that have already been searched for technosignatures — a region of the cosmos where, Mason argues, the odds of finding an artificial transmission may be higher than previously assumed.
The study was published in the Monthly Notices of the Royal Astronomical Society.
